1. Technical Field
The present invention relates to a touch panel, an electro-optic device, a manufacturing method for an electro-optic device and an electronic device.
2. Related Art
In recent years, in conjunction with the increasing use of small information electronic devices such as personal digital assistants (PDA) and palm top computers, liquid crystal display devices that have a touch panel mounted as an input device on a liquid crystal panel have become widely used.
An example of this type of touch panel is an ultrasonic surface acoustic wave system includes: a glass substrate, a transmitter that transmits a surface acoustic wave over a surface of the glass substrate, and a receiver that detects transmitted surface acoustic waves.
When a user touches a surface of the glass substrate with a finger or the like, the surface acoustic waves that are being transmitted over the surface of the glass substrate become attenuated at the touched position.
In an ultrasonic surface acoustic wave type of touch panel, it is possible to detect a position touched by a user using this property of surface acoustic waves to become attenuated at a touched position.
However, in a typical ultrasonic surface acoustic wave type of touch panel, because surface acoustic waves are generated on the topmost surface, the surface acoustic waves also become attenuated if water droplets or oil droplets, or dirt or the like are adhering to this topmost surface.
Because of this, an ultrasonic surface acoustic wave type of touch panel erroneously detects locations where water or oil droplets or dirt have adhered as positions touched by a user's finger or the like.
In a touch panel device disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-348686, because the touch panel is formed by a single glass substrate, it has poor impact resistance and when the glass has been formed as a particularly thin plate, there is a problem in that it is broken by only a slight impact.
Therefore, a touch panel has been proposed in which a transparent resin film or the like is arranged on the topmost surface of the glass substrate that is transmitting the surface acoustic waves.
For example, in Japanese Unexamined Patent Application, First Publication No. 2004-348686, a touch panel is disclosed that includes: a glass substrate over which a surface acoustic wave is transmitted; a transducer that sends and receives surface acoustic waves and is arranged facing circumferential edge portions of this glass substrate so as to form a pair; a detecting section that, based on surface acoustic waves that are sent and received by the transducer, detects a touch position of an object that is touching a predetermined operating area; and a transparent resin film that is arranged so as to sandwich a space layer between itself and the glass substrate, and that has a plurality of dot spacers formed on a surface thereof that faces the glass substrate.
In addition to a transparent resin film, a transparent glass substrate or the like is also used to protect the topmost surface of a substrate over which surface acoustic waves are transmitted.
By employing this type of touch panel structure, because the transparent substrate over which surface acoustic waves are transmitted is not exposed but is covered by a transparent resin film, it is possible to prevent any malfunctions that are caused by scratches or dirt or other contamination, and it is also possible to prevent glass substrate shards from flying should the glass substrate be broken.
In the above described patent document, the outer surface of the transparent resin film forms an input surface that is pressed by a user, and when an input is made a predetermined position of an outer surface of the transparent resin film is pressed so as to bend the transparent film.
The bending portion of the transparent resin film makes contact with the glass substrate surface and causes the surface acoustic waves being transmitted over the glass substrate surface to become attenuated.
The transducer detects a position pressed by a user based on the attenuation factor of these surface acoustic waves.
However, in a transparent resin film (glass substrate), because there is a high modulus of elasticity (Young's modulus), the resin film is not sufficiently bent by the pressing of the user and it is not possible to attenuate the surface acoustic waves being transmitted over the glass substrate surface.
As a result, there is a problem in that it has not been possible to detect the precise position pressed by a user and input malfunctions occur.